CBSE Class 10 Science Chapter 9: Heredity and Evolution NCERT Solutions

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NCERT Solutions PDF Class 10 PDF

This chapter delves into the fundamental principles of Heredity and Evolution, crucial for Class 10 Science students. The NCERT Solutions provided here break down complex concepts like how variations arise in species, particularly in asexually reproducing organisms, and their role in survival. It explains Mendel's groundbreaking experiments with pea plants, illustrating the concepts of dominant and recessive traits and how they are inherited. The solutions clarify the inheritance patterns observed in the F1 and F2 generations, providing a clear understanding of genetic principles. These solutions are designed to help students grasp the core ideas of heredity and evolution, aiding in their exam preparation by offering step-by-step explanations and clear reasoning for each question.

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Quick info

BoardCBSE
ClassClass 10
SubjectScience
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 9

Chapter summary

Chapter 9 of the CBSE Class 10 Science syllabus focuses on Heredity and Evolution. The NCERT Solutions cover the origin of variations in species, especially through asexual reproduction, and their significance for survival. It also explains Mendel's experiments, demonstrating the concepts of dominant and recessive traits and their segregation during inheritance. The solutions clarify the genotypic and phenotypic ratios observed in offspring generations, providing a solid foundation in genetics.

Learning outcomes

  • Understand the role of variations in species survival.
  • Explain how variations arise in asexually reproducing organisms.
  • Differentiate between dominant and recessive traits.
  • Analyze Mendel's experiments on pea plants.
  • Interpret the inheritance patterns in F1 and F2 generations.

Topics covered

Paper topics

  • Variations in species
  • Asexual reproduction and variation
  • Survival advantage of variations
  • Mendel's experiments
  • Dominant traits
  • Recessive traits
  • Inheritance in F1 generation
  • Inheritance in F2 generation
  • Genetics
  • Evolution

Important topics

  • Role of variations in survival
  • Mendel's laws of inheritance
  • Dominant and recessive traits
  • Inheritance patterns (F1 and F2 generations)

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Questions and Solutions

Question 1

If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Solution: In species that reproduce asexually, new individuals are formed through the copying of DNA from the parent cells. This DNA copying process is not always perfectly accurate, leading to the creation of variations. The rate at which variations appear is generally low in asexual reproduction. Therefore, a trait that is present in a larger percentage of the population, like trait B (60%), has had more time to spread and is more likely to have arisen earlier than a trait present in a smaller percentage, like trait A (10%). Conversely, trait A, being present in only 10% of the population, suggests it is a more recent variation.

Question 2

How does the creation of variations in a species promote survival?
Solution: Variations are crucial for the long-term survival of a species, especially when environmental conditions change. For instance, if the temperature of a water body suddenly increases, most bacteria living there might die. However, if some bacteria possess variations that make them resistant to higher temperatures, they will survive. These resistant variants ensure that the species does not face extinction due to the environmental change. While variations can promote the survival of the species as a whole, it's important to note that not all variations are necessarily beneficial to the individual organism; some might be neutral or even detrimental.

Question 1

How do Mendel's experiments show that traits may be dominant or recessive?
Solution: Gregor Mendel conducted experiments using pea plants to understand the inheritance of traits. He started with true-breeding plants, meaning they consistently produced offspring with the same trait (e.g., pure tall plants always produced tall offspring, and pure dwarf plants always produced dwarf offspring). Mendel crossed a true-breeding tall pea plant (represented by genotype TT) with a true-breeding dwarf pea plant (represented by genotype tt).

The seeds produced from this cross were grown, forming the first filial or F_1 generation. Interestingly, all the F_1 generation plants were tall. This indicated that the trait for tallness was expressed, while the trait for dwarfness was not.

Mendel then self-pollinated these F_1 tall plants. When he grew the plants from these self-pollinated seeds, forming the second filial or F_2 generation, he observed a different result. Out of the F_2 plants, approximately three-fourths were tall, and one-fourth were short. This reappearance of the dwarf trait in the F_2 generation, which was hidden in the F_1 generation, demonstrated that the dwarf trait was still present but masked.

Mendel concluded from these experiments that one trait (tallness) was dominant over the other trait (dwarfness). The dominant trait masks the expression of the recessive trait when both alleles are present in the F_1 generation. The recessive trait, however, reappears in the F_2 generation when the alleles segregate.

Common mistakes

  • Confusing the origin of variations with their benefit to the individual.
  • Misinterpreting the ratios in Mendel's F2 generation.
  • Assuming all variations are beneficial for survival.

Revision tips

  • Focus on understanding the link between variation and survival.
  • Draw Punnett squares to visualize Mendelian inheritance.
  • Review Mendel's experiments and their conclusions carefully.
  • Practice explaining dominant and recessive traits with examples.

Practice MCQs

Q1. In an asexually reproducing species, a trait present in 60% of the population is likely to have:

Q2. Which of the following best describes the role of variations in species survival?

Q3. According to Mendel's experiments, what happens to the recessive trait in the F1 generation when crossing pure tall and pure dwarf pea plants?

Q4. In Mendel's F2 generation from a cross of true breeding tall and dwarf plants, what is the approximate ratio of tall to short plants?

Q5. The trait that is expressed in the F1 generation from a cross between two contrasting pure traits is called:

Frequently asked questions

What is the main concept of Chapter 9, Heredity and Evolution for Class 10 Science?

Chapter 9 explains how traits are passed from parents to offspring (heredity) and how species change over time (evolution), focusing on the role of variations and Mendel's experiments.

How do variations help a species survive?

Variations provide a range of traits within a population. If the environment changes, some individuals with advantageous variations are more likely to survive and reproduce, ensuring the species' continuation.

What is the difference between dominant and recessive traits?

A dominant trait is expressed even if only one copy of the corresponding allele is present. A recessive trait is only expressed when two copies of the corresponding allele are present.

What did Mendel's experiments show about inheritance?

Mendel's experiments showed that traits are inherited in predictable patterns, with dominant and recessive traits segregating and assorting independently, leading to specific ratios in offspring generations.

Why are these NCERT Solutions helpful for Class 10 students?

These solutions provide clear, step-by-step explanations for each question, helping students understand complex concepts like heredity and evolution and prepare effectively for their exams.

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